Cycling vests and gilets are popular with bike riders of all standards from beginner to tour level. They provide warmth and wind protection in a light weight form - but without the danger of overheating from a full jacket. And when not needed they stow easily in a jersey pocket. For many they are core bicycle wear and worn in all but the warmest weather.
If your are a tour level rider - you may be able to take them on and off without stopping. For the rest of us - a set of traffic lights is often enough.